The Boy Spies of Philadelphia is a children's novel originally published in 1897 under the title With Washington at Monmouth. It is one of a series of "Boy Spies" novels dating to the 1890s and early 1900s written by James Otis Kaler (writing as James Otis) and William P. Chipman. The Boy Spies of Philadelphia tells the story of a group of boy spies who helped the Continental Army at Valley Forge.